CVE-2026-26861: Clevertap Web SDK

High severity, CVSS 8.3. EPSS: 0.2% chance of exploitation in the next 30 days.

CleverTap Web SDK version 1.15.2 and earlier is vulnerable to Cross-Site Scripting (XSS) via window.postMessage. The handleCustomHtmlPreviewPostMessageEvent function in src/util/campaignRender/nativeDisplay.js performs insufficient origin validation using the includes() method, which can be bypassed by an attacker using a subdomain

Affected products

• Clevertap Clevertap Web SDK: up to and including 1.15.2

Published 2026-02-27. Last modified 2026-06-17.